Two-piece golf shaft

ABSTRACT

Various embodiments of a two-piece golf shaft are provided, which include a hollow upper section, a hollow or solid lower section formed from an injection-molded chopped carbon fiber/thermoplastic material, and a coupling insert configured to join the lower section to the upper section (and, optionally, to the golf club head as well).

RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.63/216,466, filed Jun. 29, 2021, which is incorporated by referenceherein in its entirety.

BACKGROUND

Certain multi-piece hybrid golf shafts have been in existence for manyyears in the golf shaft industry. Examples of existing hybrid golfshafts are described, for example, in U.S Pat. Nos. 6,729,970 and6,203,447.

SUMMARY

Various embodiments of the present invention provide a two-piececomposite golf shaft comprising a hollow upper section and a hollow orsolid tip section formed from a chopped carbon fiber/thermoplastic resinmaterial. In some embodiments, the upper section and tip section may becoupled together using an attachment method and device according toembodiments of the present invention, which couples the two piecestogether to form a single shaft. This new golf shaft construction anddesign is applicable to all the different categories associated with agolf club, including, but not limited to, putter shafts, driver shafts,and iron shafts. The lower section (tip section) comprises a choppedcarbon fiber/thermoplastic resin material that can be molded intounlimited shapes and sizes and can be solid or hollow in itsconstruction. The chopped carbon fiber/thermoplastic material providesisotropic mechanical properties similar to metals and at the same timeovercomes the existing geometry limitations of current steel andcarbon/epoxy shafts. The ability to form different geometric crosssections with this chopped carbon fiber/thermoplastic material can allowfor increased strength and stiffness compared to traditional roundcross-sectional shapes associated with current steel and carbon/epoxygolf shafts. In addition to being able to mold unlimited shapes andcontours, this new technology allows for different densities that can bemolded and even allows for a gradient of density throughout the tipsection. All of these attributes, combined with excellent dampingproperties, can provide the golfer with a more stable shaft that has aunique feel compared to traditional steel and carbon/epoxy hybrid golfshafts.

In some embodiments, the invention provides a hybrid two-piece golf clubshaft comprising an upper tubular shaft section fabricated from carbonfiber composite material which is joined to a lower shaft sectionutilizing a coupling insert according to embodiments of the presentinvention. The coupling insert creates a joint wherein the axialstraightness is maintained between the upper and lower section and theresulting strength of the bond joint is dramatically increased (e.g.,due to mechanical interlocking features of the bond joint geometry).

In some embodiments, the upper shaft section is comprised of carbonfiber/epoxy composite materials to form a tubular structure.

In some embodiments, the upper shaft section has a defined longitudinalaxis configured to be aligned to the lower tip section of the shaft.

In some embodiments, the upper shaft section has a defined parallellength section along the longitudinal axis that that is located on theinner diameter of the shaft and is located in the bond joint area.

In some embodiments, the upper shaft section has a circularcross-sectional shape in the radial direction extending throughout thelongitudinal axis of the upper shaft section.

In some embodiments, the lower shaft section is comprised of acombination of short chopped carbon fiber and a thermoplastic resinwhich is then injection molded into the lower tip section.

In some embodiments, the lower shaft section is non-tubular (solid).

In some embodiments, the lower shaft section has a clearly definedlongitudinal axis that is aligned to the longitudinal axis of the uppershaft section.

In some embodiments, the lower shaft section contains four semicircularridges located at equal distance around the circumference of the bondjoint end of the lower section.

In some embodiments, the lower shaft section contains four semicircularridges located at equal distance around the circumference of the bondjoint end of the lower section that are convex shaped and slide into acorresponding set of matching concave grooves located within thecoupling insert.

In some embodiments, the lower shaft section contains four semicircularridges located at equal distance around the circumference of the headbond end that is bonded into the golf club head.

In some embodiments, the coupling insert that bonds the upper and lowersections is made of aluminum.

In some embodiments, the coupling insert that bonds the upper and lowersections is made of a carbon fiber/thermoplastic resin material (e.g.,KyronMAX).

In some embodiments, the coupling insert that bonds the upper and lowersections is made of stainless steel.

In some embodiments, the coupling insert that bonds the upper and lowersections is made of metal matrix composite.

In some embodiments, the coupling insert incorporates an indexing marklocater which aligns the lower shaft longitudinal axis to the uppershaft longitudinal axis.

In some embodiments, the coupling insert contains a flange section thatbridges between the lower and upper section that is visible afterbonding.

In some embodiments, the coupling insert contains four semicircularconcave grooves that extend on the inside diameter the full length ofthe coupling insert which accepts the four corresponding convex ridgescontained on the bond joint end of the lower tip section.

In some embodiments, the coupling insert has a shoulder on both endsthat is slightly smaller (e.g., 0.0005 inches smaller) than the internaldiameter of the upper shaft. This close to interference fit properlyaligns the coupling insert to the centerline axis of the upper shaft andprovides for perfect axial straightness between the upper and lowershaft sections.

In some embodiments, the coupling insert has a knurled surface so thatthe adhesive has a uniform bondline thickness.

In some embodiments, the lower shaft section is molded into a radialcross-sectional shape that is circular throughout the length of thelower tip section.

In some embodiments, the lower shaft section is molded into a radialcross-sectional shape that is hexagonal throughout the length of thelower tip section.

In some embodiments, the lower shaft section is molded into a radialcross-sectional shape that is octagonal throughout the length of thelower tip section.

In some embodiments, the lower shaft section is molded into a radialcross-sectional shape that is fluted with six recessed channelsthroughout the length of the lower tip section.

In some embodiments, the lower shaft section is molded into a radialcross-sectional shape that is tapered throughout the length of the lowertip section, thus increasing in diameter at the head bond end andincreasing in diameter up to the bond joint end of the lower tipsection.

In some embodiments, the lower shaft section is molded into a non-linearlongitudinal shape with a variety of axes.

In some embodiments, the lower shaft section is molded into a non-linearlongitudinal shape with a double bend or single bend shape required forputter shafts.

In some embodiments, the lower tip section can have the density of thecarbon fiber/thermoplastic resin modified to change the overall densityof the lower tip section.

In some embodiments, the lower shaft section can have a density rangingfrom 1.2 grams/cubic centimeter up to 10 grams/cubic centimeter.

In some embodiments, the lower shaft section can have a density thatvaries from a higher density at the head bond end of the lower tipsection and reducing in density moving towards the opposite end of thelower tip section.

In some embodiments, the lower tip section can be inserted into atraditional bore hole contained in all golf club heads.

In some embodiments, the lower shaft section has a hole drilled in thecenter of the lower tip section that will slide over a head design thatincorporates a solid post design instead a round bore hole.

In some embodiments, the invention provides a set of golf clubs eachgolf club in the set containing a two-piece golf club shaft as describedabove having a descending length of the lower tip section as the clublength gets shorter throughout the set of clubs.

In some embodiments, the invention provides a set of golf clubs eachgolf club in the set containing a two-piece golf club shaft as describedabove having an ascending length of the lower tip section as the clublength gets shorter throughout the set of clubs.

In some embodiments, the invention provides a set of golf clubs eachgolf club in the set containing a two-piece golf club shaft as describedabove having a constant length of the lower tip section as the clublength gets shorter throughout the set of clubs.

In some embodiments, the lower shaft section is tubular in nature, withan outer diameter that matches the inner diameter of the upper sectionof the golf shaft allowing it to be installed directly into the uppersection by simply bonding the lower section into the upper section. Insome embodiments a universal coupler comprising machined aluminum,titanium, or steel, or an injection-molded composite material, could beused that fits internally and externally on the upper and lower sectionsof the golf shaft, respectively.

In some embodiments, the invention provides a two-piece golf shaft,comprising a hollow upper section; a hollow or solid lower section; anda coupling insert configured to join the upper section and the lowersection together, wherein the lower section is formed from aninjection-molded carbon fiber-reinforced thermoplastic material, andwherein the coupling insert comprises a hollow structure configured tofit into an inner diameter of the upper section and configured toreceive an end of the lower section inserted therein.

In some embodiments, the carbon-reinforced thermoplastic materialcomprises short length chopped carbon fiber and thermoplastic resin.

In some embodiments, the carbon-reinforced thermoplastic materialcomprises about 30% to about 50% chopped carbon fiber.

In some embodiments, the carbon-reinforced thermoplastic materialcomprises a polyamide thermoplastic resin or derivative thereof

In some embodiments, at least one end of the lower section has anexterior surface configured to mate with an interior surface of thecoupling insert.

In some embodiments, the exterior surface of at least one end of thelower section and at least a portion of the interior surface of thecoupling insert are smooth.

In some embodiments, the exterior surface of at least one end of thelower section comprises a plurality of convex ridges configured to matewith a plurality of concave grooves on the interior surface of thecoupling insert.

In some embodiments, the coupling insert is formed from a machined metalor alloy.

In some embodiments, the coupling insert comprises aluminum, titanium,or stainless steel.

In some embodiments, the coupling insert is formed from aninjection-molded carbon fiber-reinforced thermoplastic material or metalmesh composite material.

In some embodiments, the coupling insert includes a flange or headportion on one end, the flange or head portion configured to form abridge that is visible between the upper section and the lower sectionafter they are joined together.

In some embodiments, the coupling insert has an exterior surfacecomprising at least one shoulder configured to provide an interferencefit with the inner diameter of the upper section.

In some embodiments, the coupling insert has an exterior surfacecomprising a knurled surface on at least a portion thereof.

In some embodiments, the lower section has a cross-sectional shape thatis circular, hexagonal, octagonal, or fluted.

In some embodiments, the lower section is hollow.

In some embodiments, the lower section is tapered, decreasing indiameter from a proximal end toward a distal end thereof.

In some embodiments, the lower section is molded into a non-linear shapewith a variety of longitudinal axes.

In some embodiments, the lower section has a density ranging from about1.2 grams/cubic centimeter to about 10 grams/cubic centimeter.

In some embodiments, the lower section has a density gradient, wherebythe density increases from a proximal end toward a distal end thereof.

In some embodiments, the lower section includes a metal mesh or rod.

Additional features and advantages of embodiments of the presentinvention are described further below. This summary section is meantmerely to illustrate certain features of embodiments of the invention,and is not meant to limit the scope of the invention in any way. Thefailure to discuss a specific feature or embodiment of the invention, orthe inclusion of one or more features in this summary section, shouldnot be construed to limit the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing summary, as well as the following detailed description ofcertain embodiments of the application, will be better understood whenread in conjunction with the appended drawings. For the purposes ofillustrating the systems and methods of the present application, thereare shown in the drawings preferred embodiments. It should beunderstood, however, that the application is not limited to the precisearrangements and instrumentalities shown. In the drawings:

FIG. 1 is a perspective view of an illustrative golf club (putter),including a putter head, a grip, and a two-piece shaft according tovarious embodiments of the present invention;

FIG. 2 is a perspective view of an illustrative golf club (iron),including an iron head, a grip, and a two-piece shaft according tovarious embodiments of the present invention;

FIG. 3 is a perspective view of an illustrative golf club (driver),including a driver head, a grip, and a two-piece shaft according tovarious embodiments of the present invention;

FIG. 4A is an exploded view of a putter shaft according to variousembodiments of the present invention, configured to be bonded into afemale opening on the putter head; FIG. 4B is an exploded view of aputter shaft according to various embodiments of the present invention,configured to be bonded into a female opening on the putter head;

FIG. 5 is an exploded view of a putter shaft according to variousembodiments of the present invention, configured to be bonded into afemale opening on the putter head utilizing a second coupler insert;

FIG. 6 is an exploded view of a putter shaft according to variousembodiments of the present invention, configured to be bonded over acylindrical metallic post on the putter head utilizing a second couplerinsert;

FIG. 7 is an exploded view of a putter shaft according to variousembodiments of the present invention, configured to be bonded over acylindrical metallic post on the putter head;

FIG. 8A is a detail view of a tip section of a putter shaft according tovarious embodiments of the present invention, configured to be bonded toboth the upper section of the hollow shaft and the putter head itselfwith a female bond joint;

FIG. 8B is a detail view of a tip section of a putter shaft according tovarious embodiments of the present invention;

FIG. 8C is a detail view of a tip section of a putter shaft according tovarious embodiments of the present invention;

FIG. 8D is a detail view of a tip section of a putter shaft according tovarious embodiments of the present invention;

FIG. 9A is a detail view of a tip section of a putter shaft according tovarious embodiments of the present invention, configured to be bonded toboth the upper section of the hollow shaft and the putter head itselfwith an over post bond joint;

FIG. 9B is a detail view of a tip section of a putter shaft according tovarious embodiments of the present invention;

FIG. 10A is a cross-sectional view of the center of the longitudinalaxis of the tip section of FIG. 9A, which has a circular geometry thatis tapered from the large end to the smaller end;

FIG. 10B is a cross-sectional view of the center of the longitudinalaxis of the tip section of FIG. 9B, which has a circular geometry thatis tapered from the large end to the smaller end;

FIG. 11A is a detail view of a tip section of a putter shaft accordingto various embodiments of the present invention, configured to be bondedto both the upper section of the hollow shaft and the putter head itselfwith a female bond joint;

FIG. 11B is a detail view of a tip section of a putter shaft accordingto various embodiments of the present invention;

FIG. 12A is a detail view of a tip section of a putter shaft accordingto various embodiments of the present invention, configured to be bondedto both the upper section of the hollow shaft and the putter head itselfwith an over post bond joint;

FIG. 12B is a detail view of a tip section of a putter shaft accordingto various embodiments of the present invention;

FIG. 12C is a detail view of a tip section of a putter shaft accordingto various embodiments of the present invention;

FIG. 12D is a detail view of a tip section of a putter shaft accordingto various embodiments of the present invention;

FIG. 13A is a cross-sectional view of the center of the longitudinalaxis of the tip section of FIG. 12A, which has a hexagonal geometryconsisting of six symmetric flat sides that are tapered from the largeend to the smaller end;

FIG. 13B is a cross-sectional view of the center of the longitudinalaxis of the tip section of FIG. 12B, which has a hexagonal geometryconsisting of six symmetric flat sides that are tapered from the largeend to the smaller end;

FIG. 14A is a detail view of a tip section of a putter shaft accordingto various embodiments of the present invention, configured to be bondedto both the upper section of the hollow shaft and the putter head itselfwith an over post bond joint;

FIG. 14B is a detail view of a tip section of a putter shaft accordingto various embodiments of the present invention;

FIG. 14C is a detail view of a tip section of a putter shaft accordingto various embodiments of the present invention;

FIG. 14D is a detail view of a tip section of a putter shaft accordingto various embodiments of the present invention;

FIG. 15A is a detail view of a tip section of a putter shaft accordingto various embodiments of the present invention, configured to be bondedto both the upper section of the hollow shaft and the putter head itselfwith a female bond joint;

FIG. 15B is a detail view of a tip section of a putter shaft accordingto various embodiments of the present invention;

FIG. 16A is a cross-sectional view of the center of the longitudinalaxis of the tip section of FIG. 15A, which has a fluted geometryconsisting of six semicircular flutes that are tapered from the largeend to the smaller end;

FIG. 16B is a cross-sectional view of the center of the longitudinalaxis of the tip section of FIG. 15B, which has a fluted geometryconsisting of six semicircular flutes that are tapered from the largeend to the smaller end;

FIG. 17 is a detail view of a tip section of a putter shaft according tovarious embodiments of the present invention, configured to be bonded toboth the upper section of the hollow shaft and the putter head itselfwith a female bond joint, the longitudinal axis having a double bendinggeometry;

FIG. 18A is a detail view of a tip section of a putter shaft accordingto various embodiments of the present invention, configured to be bondedto both the upper section of the hollow shaft and the putter head itselfwith an over post bond joint, the longitudinal axis having a doublebending geometry;

FIG. 18B is a detail view of a tip section of a putter shaft accordingto various embodiments of the present invention, configured to be bondedto both the upper section of the hollow shaft and the putter head itselfwith an over post bond joint, the longitudinal axis having a doublebending geometry;

FIG. 19 is a cross-sectional view of the center of the longitudinal axisof the tip section of FIG. 18A, which has a circular geometry that istapered from the large end to the smaller end;

FIG. 20A is a cross-sectional isometric view of a tip section of aputter shaft according to various embodiments of the present invention,which is reinforced with a layer of metal mesh;

FIG. 20B is a detail view of a tip section of a putter shaft accordingto various embodiments of the present invention, depicting a gradient ofdensity from the head bond joint end to the upper bond joint into theupper shaft section;

FIG. 20C is a detail view of a tip section of a putter shaft accordingto various embodiments of the present invention, depicting a gradient ofdensity from the head bond joint end to the upper bond joint into theupper shaft section;

FIG. 21 shows three different views of a coupling insert for a two-pieceshaft according to various embodiments of the present invention,configured to bond the lower tip section to the upper shaft section;

FIG. 22 is a cross-sectional end view of the coupling insert of FIG. 21, showing the four semicircle channels that the lower section locks andbonds into;

FIG. 23 is a cross-sectional front view of the coupling insert of FIG.21 , showing the four semicircle channels that the lower section locksand bonds into;

FIG. 24 is a cross-sectional view of the reverse geometry of thecoupling insert that is contained on one or both ends of the lower tipsection of a two-piece shaft according to various embodiments of thepresent invention, providing a mechanical interlock between the lowerand upper section;

FIG. 25 shows five different views of a coupling insert for a two-pieceshaft according to various embodiments of the present invention,configured to bond the lower tip section to the upper shaft section;

FIG. 26A is an illustrative array of iron golf clubs forming a set thatcontains a descending overall shaft length coupled with a descendinglength of the lower tip section of a two-piece shaft according tovarious embodiments of the present invention;

FIG. 26B is an exploded view of an iron shaft according to variousembodiments of the present invention;

FIG. 27A is an illustrative array of driver golf clubs forming a setthat contains a descending overall shaft length coupled with adescending length of the lower tip section of a two-piece shaftaccording to various embodiments of the present invention; and

FIG. 27B is an exploded view of a driver shaft according to variousembodiments of the present invention.

DETAILED DESCRIPTION

As noted above, certain multi-piece hybrid golf shafts have been inexistence for many years in the golf shaft industry. Examples ofexisting hybrid composite/metal golf shafts are described, for example,in U.S. Pat. Nos. 6,729,970 and 6,203,447. The shafts described in thosepatents rely on bonding a steel tip section that is hollow, to acomposite upper section shaft that is also hollow. The two sections arebonded together using a coupling ferrule that is adhesively bonded tothe internal diameters of both the upper and lower sections. Theferrules are constructed using a carbon/epoxy composite material that isglued into both ends of the steel tip section and the composite uppersection. The prior art ferrules are very simplistic in their design andonly provide for coupling the two different sections together. They donot provide for any mechanical indexing between the upper section andthe lower section. Furthermore, in most cases the ferrule is bonded intothe upper section of the composite shaft that has very thin wallthicknesses which causes a weak point in the overall shaft and is proneto failure at the joint intersection.

The theory behind using a steel tip hollow section in the tip of hybridtwo-piece shafts is that steel provides for very low torque values andhas a density that is four to five times that of carbon/epoxy material.The lower torque values improve the performance of the overall club byminimizing the twisting of the shaft especially in off center ballstrike locations. The heavier density located near the head, increasesthe mass distribution of the overall club by shifting the center ofgravity towards the golf club head. This also helps in terms ofcounterbalancing the overall club. The other reason that steel has beenused in hybrid golf shafts is for putter shaft applications that requirethe tip section of the shaft to have complex bend geometries fordifferent types of putter head offsets. Steel is relatively easy to formand bend to some of the complex geometries, whereas graphite shafts arevery restricted in terms of complex bend geometries. This is due to someof the process limitations of carbon tubular structures and the costsassociated with manufacturing carbon/epoxy golf shafts with complexshapes.

The current hybrid golf shafts in the market today have been limited tocircular longitudinal cross-sectional geometries formed from steel.Apart from the benefit of being able to form a hollow steel tip sectionof existing hybrid composite/steel golf shafts into complex bendgeometries, steel has significant limitations in wall thickness andformability to form into alternate cross-sectional shapes. A circularcross section in hollow steel shafts is a common shape; however, forminga steel golf shaft into longitudinal cross-sectional shapes like ahexagon, octagon, fluted, etc. is extremely challenging since theseparts are tapered and very thin-walled structures. The result in tryingto form hollow steel golf shafts or steel tip sections of golf shaftsinto complex cross-sectional shapes can cause metal fatigue, crackingand generally structurally weak designs.

As mentioned in U.S. Pat. No. 6,203,447, prior art hybrid modular golfshafts that have a steel segment and a composite segment are prone togalvanic corrosion in the area where the two shafts are joined when inthe presence of moisture, especially high salinity moisture commonlyfound near golf courses near a salt water source. This type of corrosioncan not only cause a visible outward area of corrosion, but alsosignificantly weaken the bond joint area. Prior methods to overcome thisscenario have utilized placing glass beads in the epoxy bond joint tominimize contact between the steel portion of the golf shaft and thecomposite segment in addition to using a plastic ferrule that isnonconductive.

The present invention provides, in various embodiments, a hybridtwo-piece golf shaft that can overcome the above-described deficiencies,and can provide, for example, for a variety of cross-sectionalgeometries, a variety of longitudinal axis profiles, an increase instrength, and/or a lowering of torque values in the tip section, ascompared to existing products in the art. In various embodiments of thepresent invention, the lower section of the two-piece shaft can beaccurately bonded to the upper section via a coupling insert that canprovide for essentially perfect alignment between the two sections, canreduce/eliminate the galvanic corrosion scenario described above, and/orcan position the shaft in the desired location within the head itself.

Various embodiments of the present invention provide for a lightweighthybrid composite/thermoplastic tip golf shaft construction for a varietyof various golf club types. The types of golf clubs where the presentinvention is applicable include drivers, irons, and putters.

In some embodiments, the present invention includes a hybrid shaftconstruction comprising a hollow (tubular) composite shaft uppersection, and a lower section that is made from a chopped carbonfiber/thermoplastic resin material (solid or hollow), the two sectionscoupled together with a coupling insert according to embodiments of thepresent invention.

The upper composite shaft section may be manufactured similar toexisting full-length one-piece golf shafts and may utilize similarmaterials to the current art (such as, but not limited to, traditionalcarbon fiber sheets or the metal mesh composite materials described inU.S. patent application Ser. No. 17/165,721, which is incorporated byreference herein in its entirety). The outer diameters and innerdiameters along with the lengths of the composite upper section can varydepending on the end use application of the golf club. In essence, acomposite upper section of an iron shaft, for example, will inherentlybe longer in length compared to an upper section of a putter shaft giventhe overall lengths of the two different clubs. In some embodiments, theupper section shaft outer diameter where the shaft meets up with thelower section may have the same outer diameter of the adjoining lowertip section when it is bonded together yielding a uniform bond jointbetween the lower and upper section. However, in other embodiments, thelower section outer diameter could be larger or smaller in diametercompared to the outer diameter of the upper section where the jointoccurs.

In some embodiments, the upper composite tubular shaft segment maycontain a parallel internal diameter (e.g., for a minimum of about twoinches) that is located in the bond joint end of the upper section. Thisprovides a uniform region for the coupling insert to be adhesivelybonded into. This parallel section can allow the coupling insert to seatproperly which can help in maintaining the lower section alignment.

In some embodiments, the upper composite shaft section is a lightweightcomposite shaft which helps add to the counterbalance properties of theoverall club in addition to reducing the overall weight of the golf clubthus increasing the swing speed of the club equating to increaseddistance especially in driver clubs.

In some embodiments, the lower tip section of the shaft is made from acombination of blending short length chopped carbon fiber with athermoplastic resin (such as, but not limited to, the KyronMAX compoundsprovided by Mitsubishi Chemical Advanced Materials). This compositethermoplastic segment of the two-piece hybrid construction can bemanufactured via an injection molding process commonly used to fabricatemany plastic parts. In some embodiments, the preferred plastic ispolyamide and derivatives of polyamide thermoplastic resin. Polyamidehas a favorable blend of mechanical properties and surface finish forthis application. However, there are many other types of plasticmaterials that can be used in other embodiments, including, but notlimited to: polyimide polycarbonate, nylon, polypropylene, etc. Animportant feature of this material technology is the process involvedwith the accurate blending of the carbon fiber reinforcement and theplastic resin prior to the combined material going through the injectionmolding process. In certain preferred embodiments, the fiber volume toresin ratio is approximately 30% carbon and 70% thermoplastic resin. Inother embodiments, the ratio of carbon fiber to thermoplastic resin canbe increased to as high as 50% if desired; however, increasing the fiberratio to this level can create a surface finish that is not desirableand difficult to paint. Therefore, in some embodiments, the preferredfiber to resin ratio is about 30% carbon. Even at a 30% fiber ratio,this material can achieve virtual isotropic properties that are similarto 7075 T6 aluminum. Unlike continuous carbon fiber/epoxy structuresthat are extremely anisotropic in nature, the chopped carbonfiber/thermoplastic resin material (e.g., KyronMAX) used in embodimentsof the present invention exhibits the same properties in all directions.

In various embodiments of the present invention, due to the nature of aninjection molding process, as well as the chopped carbon/thermoplasticmaterial, it is possible to mold not just a simple circular shaped crosssection in the tip section, but virtually any cross-sectional shapedesired. This is very hard and costly to achieve with continuousreinforced carbon/epoxy materials in addition to steel. As shown in thedrawings (described further below), a variety of cross-sectional shapesmay be used in this application. These shapes include, but are notlimited to, hexagonal, fluted, and octagonal shapes among others. All ofthese shapes may include a tapering section from large to smallextending from the bond joint end towards the extreme tip of the overallgolf shaft. Trying to achieve a complex geometry while at the same timeadding in a taper increases the complexity in the manufacturing of theseshapes substantially. Trying to achieve these types of shapes utilizingsteel golf shaft construction techniques or continuous carbonfiber/epoxy golf shaft construction techniques would be extremelydifficult, costly, and prone to mechanical failure. One of the mainbenefits of an injection molding process according to embodiments of thepresent invention, is that the processing techniques yield a low cost,extremely consistent part with all the benefits of a thermoplasticmaterial.

Utilizing an injection molding process with a chopped carbonfiber/thermoplastic material as described herein not only allows fordifferent cross-sectional shapes as mentioned above, but it allows fordifferent longitudinal geometries beyond just manufacturing a straighttip section. This is especially pertinent when one looks at thedifferent putter shaft shapes that are within the current art. Manyputters are designed to have what is called an offset between theneutral axis of the golf shaft and the location of the putter head. Thiscan be seen with double and single bend putter shaft on the markettoday. The offset helps golfers align the putter head in a differentfashion than a straight shafted putter. The key point is, thatmanufacturing a straight tapered tip cross section with differentcross-sectional shapes is a difficult and cost prohibitive process whenutilizing continuous carbon fiber/epoxy or steel materials. Now couplethis with then adding another axis change like a double bend puttershape, and the process becomes unviable unless an injection mold orcompression mold process is utilized. In an alternate embodiment, onecould use a sheet molding compound (SMC) with a compression moldingprocess to achieve similar types of complex geometries. However, usingan SMC does not achieve the same isotropic nor damping properties thatcan be achieved with chopped carbon fiber/thermoplastic materials.

A further benefit of embodiments of the present invention with respectto the chopped carbon fiber/thermoplastic resin material is the strengthof the tip. Unlike tubular steel and composite shafts used in existinghybrid two-piece golf shafts, embodiments of the present invention mayhave a hollow or solid tip section comprised of 100% chopped carbonfiber/thermoplastic material. The chopped carbon fiber/thermoplastic tipsection can provide, for example, for increased strength, increasedmass, and/or increased stiffness and stability compared to tubular steelstructures. This is especially true when adding different geometriccross-sectional shapes like a fluted or hexagonal shape.

Still another benefit of various embodiments of the present invention,is that the ends of the lower tip section itself may have a geometricdesign that provides for a mechanical locking joint into a couplinginsert according to embodiments of the invention, which may be bonded,for example, to the inside of the upper shaft section. Thermoplasticmaterials in general can be difficult to adhesively bond together tolike materials or even dissimilar materials by relying on just theadhesive to provide sufficient bond strength. Therefore, shaftsaccording to various embodiments of the present invention do not solelyrely on adhesive providing the necessary bond strength required for thebond joint, but may also include a mechanical interlock that can helpeliminate the possibility of the lower shaft section debonding from thecoupler insert and the upper section. In certain preferred embodiments,four equal distant semicircular concave features are placed at the endwhich is bonded into the coupling insert. Once pressed in and curedalong with the use of an adhesive material, the ability to debond andfail in the joint area under normal playing conditions is virtuallyeliminated. This construction can also aid in the alignment between thelower section and the upper section providing for essentially perfectaxial straightness between the upper shaft and the lower tip section.This mechanical alignment can be especially critical when one isaligning a lower section that has a complex axial geometry, like adouble bend putter shaft. It is understood that there are numerouspotential geometric shapes other than a semicircle that one could use toachieve a mechanical interlock, however this is a preferred design basedupon molding difficulty and cost. In some cases, there can be amechanical interlock not just between the two shaft segments, but alsointo the head itself using a similar type of coupling insert.

Yet another benefit of utilizing a lower tip construction with choppedcarbon fiber/thermoplastic material, is that the density of theresulting combined short chopped carbon fiber and thermoplastic resincan be varied over a wide range. In various embodiments, the netresulting density on the light side may be approximately 1.4 grams/cubiccentimeter and can be increased up to approximately 10 grams/cubiccentimeter by adding a dense filler material like tungsten to achievehigher densities. As is shown in the drawings, the density can beincreased throughout the length of the tip section in a uniform density,or can be varied throughout the length of the tip section generating adenser section at the extreme tip and a lighter density moving uptowards the bond joint region. The performance benefit of the overallgolf club is to increase the counterbalance properties by shifting moremass towards the club head itself.

A further benefit of utilizing the chopped carbon fiber/thermoplasticmaterial in this application, is that it dampens the modal vibrationsthat are generated from striking a golf ball that end up transmitting upthe shaft into the hands of the golfer. The damping properties alongwith the aforementioned benefits make this an ideal material for thisapplication.

Another aspect of embodiments of the present invention centers around acoupling insert that joins the lower section to the upper section. Asmentioned in prior art examples, commonly used ferrules have beenutilized to join the upper and lower segments of hybrid golf shafts.These ferrules are usually constructed from a smaller tubular compositetube that is bonded to the internal diameters of the two sections. Thepresent invention, in various embodiments, provides a coupling insertthat may be metallic in design and is first bonded to the upper shaftsection and may be located on a specific axis identified by a locator onthe shaft itself. This reference locator point is usually the graphicsthat are applied to the upper section of the composite shaft. In certainpreferred embodiments, the coupling insert is made out of machinedaluminum or alloy thereof (e.g., 6061, 6062, or 7001 aluminum), but inother embodiments may be injection molded and may comprise carbon fiberreinforced thermoplastic resin (e.g., KyronMAX), other thermoplasticmaterials, and/or other metals (titanium, stainless steel, etc.) oralloys. As shown in the drawings, the coupling insert can vary in lengthand diameter based upon where it is bonded into the two shaft segments.This can vary based upon whether the shaft is a driver, iron, or puttershaft. In certain preferred embodiments, the coupler insert isapproximately two inches long which is sufficient length to transfer theloads and maintain stiffness in the joint area. In some embodiments, theinside of the coupling insert has four symmetric concave semicirclesthat match the geometry and size of the bond end of the lower tipsection. These four concave semicircles align with the four concavesemicircles located on the tip section so that the two piecesmechanically interlock and eliminate any variation in the axialalignment of the two shaft segments. The four concave semicircleslocated on the lower tip section create a close to interference fit whenpressed in, creating an in situ alignment mechanism. In otherembodiments, the inside of the coupling insert and the bond end of thelower tip section may be configured for a smooth interference fit. Thesurrounding bond area is adhesively bonded providing additionalstrength. The coupling insert has a wider flange or head section on theend which creates a bridge between the upper and lower shaft sections.This coupler insert can be anodized a color to both seal the aluminumand proved for an aesthetically appealing look in the joint area.

Given the above explanation of the key elements of embodiments of thepresent invention and how they relate to the shaft itself, one can nowenvision different applications of this invention and how those elementsmight be applied to a set of irons or a set of drivers including fairwaywoods. Specifically, within a set of iron shafts or driver and fairwayshafts the hybrid shaft lengths can vary along with the individuallengths of both the upper and lower sections. This can create adescending location of the bond joint region or an ascending location ofthe bond joint region. This can be done to achieve low launch angle tohigh launch angles by simply changing the location of the bond jointarea.

Further configurations and details of various embodiments of the presentinvention will become apparent in the drawings provided herewith and thedetailed descriptions provided below. The following detaileddescriptions of the drawings are meant to explain the details of certainpreferred embodiments and are not intended to limit the scope of theinvention to the described uses. In the embodiments shown in thedrawings, the lower tip sections are constructed using a chopped carbonfiber reinforced thermoplastic resin (such as, but not limited to, theKyronMAX compounds provided by Mitsubishi Chemical Advanced Materials);however, in other embodiments, different composite materials (existingor to be developed) may be used, provided they can be injection moldedinto shaft sections as described herein.

FIG. 1 illustrates a putter club and contains a hybrid shaft 2 of anillustrative embodiment of the invention. The darker area of 2represents the composite upper section of the shaft and the lightersection at the bottom represents the lower tip section of the hybridshaft. The putter head 5 is bonded to the lower tip section of the cluband the putter grip is represented by 1 that is bonded to the uppersection.

FIG. 2 illustrates an iron club and contains a hybrid shaft 3 of anillustrative embodiment of the invention. The darker area of 3represents the composite upper section of the shaft and the lightersection at the bottom represents the lower tip section of the hybridshaft, The iron head 6 is bonded to the lower tip section of the cluband the putter grip is represented by 1 that is bonded to the uppersection.

FIG. 3 illustrates a driver club and contains a hybrid shaft 4 of apreferred embodiment of the invention. The darker area of 4 representsthe composite upper section of the shaft and the lighter section at thebottom represents the lower tip section of the hybrid shaft. The driverhead 44 is bonded to the lower tip section of the club and the puttergrip is represented by 1 that is bonded to the upper section.

FIG. 4A is a schematic view of the key components that make up a hybridputter shaft according to various embodiments of the invention. Theputter head 5 is what is called a “Plumbers Neck” design which simplymeans that the putter shaft is bonded into a female opening where thetip of the hybrid putter shaft is bonded into. In this scenariodepicted, the tip of the shaft 9 is adhesively bonded into the putterhead bore hole, and a feature that may function as a means for gluerelief 43 is provided. The feature that may function as a means for gluerelief may comprise, for example, a hole that is machined into the headend of the solid tip section. In some embodiments, the hole may berelatively shallow (e.g., configured specifically to accommodate for asmall amount of excess glue to escape and go up a portion of the tipsection); however, in other embodiments the hole may be deeper (e.g.,similar to or essentially the same as the hole described and shownherein for “Over Post” designs). In other embodiments, the tip of theshaft 9 for the “Plumbers Neck” design may be smooth (e.g., as in FIG.8A). The cross section of the hybrid shaft tip section 9 is depictedhaving a hexagonal cross section in the radial direction. At the jointend of the lower tip section, exists four semicircular concave ridgesthat slide into the coupler insert 8. The coupler insert is adhesivelybonded into the upper shaft section 7 prior to bonding in the lower tipsection 9. These three components 7, 8, 9 constitute the hybrid shaftfor this configuration.

FIG. 5 is a schematic view of the key components that make up a hybridputter shaft according to various other embodiments of the invention.The putter head 5 is what is called a “Plumbers Neck” design whichsimply means that the putter shaft is bonded into a female opening wherethe tip of the hybrid putter shaft is bonded into. In this scenariodepicted, the tip of the shaft 10 is adhesively bonded into the couplerinsert 8 which is then bonded into the putter head bore hole. The crosssection of the hybrid shaft tip section 10 is depicted having ahexagonal cross section in the radial direction. At the joint end andthe head end of the lower tip section, exists four semicircular concaveridges that slide into the coupler inserts 8. The coupler insert 8 atthe joint end is adhesively bonded into the upper shaft section 7 priorto bonding in the lower tip section 10. These three components 7, 8, 10constitute the hybrid shaft for this configuration.

In other embodiments, different hybrid shaft tip sections may be usedfor the putter shafts, which utilize different cross sections and/ordifferent coupling inserts according to other embodiments of theinvention. For example, as shown in FIG. 4B, a hybrid shaft tip section20 may be used, which may be assembled with putter head 5 and uppershaft section 7 as described above for hybrid shaft tip section 9, buthas a circular cross section in the radial direction, and has a smoothjoint end that is configured to slide into a coupler insert 24. Thesethree components 7, 24, 20 constitute the hybrid shaft for thisconfiguration.

FIG. 6 is a schematic view of the key components that make up a hybridputter shaft according to additional embodiments of the invention. Theputter head 11 is what is called a “Over Post” design which simply meansthat the putter shaft is bonded onto a male post extending up from theshank of the putter head 11. In this configuration, the solid tip lowershaft section 12 has a hole machined into the solid tip section that isconstructed and arranged to slip over the metal post located at the topof the putter head 11 shank and is adhesively bonded to the couplerinsert 8 and to the putter head 11. The cross section of the hybridshaft tip section 12 is depicted having a hexagonal cross section in theradial direction. At the joint end and at the head end of the lower tipsection 12, exists four semicircular concave ridges that slide into thecoupler inserts 8. The coupler insert 8 at the joint end is adhesivelybonded into the upper shaft section 7 prior to bonding in the lower tipsection 12 and then the coupler insert 8 at the head end is adhesivelybonded over the steel post of the putter head 11. These three components7, 8, 12 constitute the hybrid shaft for this configuration.

FIG. 7 is a schematic view of the key components that make up a hybridputter shaft according to other embodiments of the invention. The putterhead 11 is what is called a “Over Post” design which simply means thatthe putter shaft is bonded onto a male post extending up from the shankof the putter head 11. In this configuration, the solid tip lower shaftsection 13 has a hole machined into the solid tip section that isconstructed and arranged to slip over the metal post located at the topof the putter head 11 shank and is adhesively bonded to the putter head11. The cross section of the hybrid shaft tip section 13 is depictedhaving a hexagonal cross section in the radial direction. At the jointend of the lower tip section 13, exists four semicircular concave ridgesthat slide into the coupler insert 8. The coupler insert is adhesivelybonded into the upper shaft section 7 prior to bonding in the lower tipsection 13 and then the head end of the lower tip section 13 isadhesively bonded over the steel post of the putter head 11. These threecomponents 7, 8, 13 constitute the hybrid shaft for this configuration.

FIG. 8A is an isometric view of an illustrative embodiment of a lowertip section 14. In this particular view, the solid tip section containsa joint end 18 with four convex semicircles that slide into the couplerinsert 8 which then is bonded into the upper shaft section 7. The headbond end 16 is a smooth surface with the absence of a hole drilled intothe tip. This is an example of a bond end designed for a “Plumbers Neck”5 or female bore into the head itself. In other embodiments, a featurethat may function as a means for glue relief may be provided in the“Plumbers Neck” design (e.g., as described above in connection with FIG.4A), or a head bond end 19 may be provided for an “Over Post” design(e.g., with a hole constructed and arranged to slip over the metal postlocated at the top of the club head, as in FIG. 12A).

FIG. 9A is an isometric view of another illustrative embodiment of alower tip section 14. In this particular view, the solid tip sectioncontains a joint end 18 with four convex semicircles that slide into thecoupler insert 8 which then is bonded into the upper shaft section 7.The head bond end 17 also is configured with four convex semicirclesthat will slide into a coupler insert 8 and then is bonded over the headpost 11. This is an example of a bond end designed for “Over Post” 11head designs. In other embodiments, the head bond end 18 may be providedfor a “Plumber's Neck” design (e.g., with a smooth end surface as inFIG. 11A).

As will be appreciated by one of skill in the art, lower tip sectionswith different cross-sectional geometries (circular, hexagonal, fluted,etc.) according to embodiments of the invention can have variouscombinations of joint end and head bond end. For example, FIG. 8B showsa circular lower tip section 14 with head bond end 16 analogous to FIG.8A, but with a smooth joint end 15 that is configured to slide into acoupler insert 24. According to various embodiments of the invention, alower tip section 14, 21, 22 or 23 with a joint end 15 or 18 (for usewith a coupling insert 8 or 24) may have a head bond end configured fora “Plumbers Neck” 5 head design (with or without a feature that mayfunction as a means for glue relief) or an “Over Post” 11 head design,and may be configured for use with or without a second coupling insert 8or 24.

FIG. 10A is a cross-sectional view of the radial geometry of the lowertip section 14 examples according to some embodiments. In thisconfiguration, the radial cross section is solid circular and it isconceived that there are multiple variants possible of the radialcross-section covered for this invention. It is also expected that mostif not all of the lower tip sections are tapering from the head bond endand increasing in diameter to the bond joint end where the upper andlower shaft sections are bonded together.

In other illustrative embodiments, as shown for example in FIG. 10B, thelower tip section 14 may be hollow. FIGS. 8C, 8D, and 9B showembodiments analogous to those depicted in FIGS. 8A, 8B, and 9A,respectively, but wherein the lower tip section 14 has a hollow circularcross section in the radial direction (as indicated by the dottedlines).

FIG. 11A is an isometric view of an illustrative embodiment of a lowertip section 21. In this particular view, the solid tip section containsa joint end 18 with four convex semicircles that slide into the couplerinsert 8 which then is bonded into the upper shaft section 7. The headbond end 18 also is configured with four convex semicircles that willslide into a coupler insert 8. This is an example of a bond end designedfor a “Plumbers Neck” 5 or female bore into the head itself. See, forexample, the exploded view of FIG. 5 (where the tip section embodimentof FIG.11A is indicated at numeral 10). If a second coupler insert isnot utilized, a head bond end 16 may be provided (e.g., as in FIG. 8A),and either 16 or 18 may be optionally provided with a feature that mayfunction as a means for glue relief (e.g., as described above inconnection with FIG. 4A).

FIG. 12A is an isometric view of another illustrative embodiment of alower tip section 21. In this particular view, the solid tip sectioncontains a joint end 18 with four convex semicircles that slide into thecoupler insert 8 which then is bonded into the upper shaft section 7.The head bond end 19 is a smooth surface with a hole drilled in thecenter that is constructed and arranged to be bonded over the head post11. This is an example of a bond end designed for “Over Post” 11 headdesigns. If a second coupler insert 8 is utilized, a head bond end 17may be provided (e.g., as in FIG. 9A).

As described above, lower tip sections according to embodiments of theinvention can have various combinations of cross-sectional geometry,joint end and head bond end. For example, FIG. 12B shows a hexagonallower tip section 21 with head bond end 19 analogous to FIG. 12A, butwith a smooth joint end 15 that is configured to slide into a couplerinsert 24.

FIG. 13A is a cross-sectional view of the radial geometry of the lowertip section 21 examples according to some embodiments. In thisconfiguration, the radial cross section is solid hexagonal and it isconceived that there are multiple variants possible of the radialcross-section covered for this invention. It is also expected that mostif not all of the lower tip sections are tapering from the head bond endand increasing in diameter to the bond joint end where the upper andlower shaft sections are bonded together.

In other illustrative embodiments, as shown for example in FIG. 13B, thelower tip section 21 may be hollow. FIGS. 11B, 12C, and 12D showembodiments analogous to those depicted in FIGS. 11A, 12A, and 12B,respectively, but wherein the lower tip section 21 has a hollowhexagonal cross section in the radial direction (as indicated by thedotted lines).

FIG. 14A is an isometric view of an illustrative embodiment of a lowertip section 22. In this particular view, the solid tip section containsa joint end 18 with four convex semicircles that slide into the couplerinsert 8 which then is bonded into the upper shaft section 7. The headbond end 19 is a smooth surface with a hole drilled in the center thatis constructed and arranged to be bonded over the head post 11. This isan example of a bond end designed for “Over Post” 11 head designs. If asecond coupler insert 8 is utilized, a head bond end 17 may be provided(e.g., as in FIG. 9A). As shown by the contrast between the darker andlighter areas of this view, the flutes contained within this design arerecessed from the outer surface of the lower tip section. These flutesor troughs extend only in the non-bond area and extend from the tip ofthe lower tip section up to the bond joint region where the two shaftsare bonded together.

FIG. 15A is an isometric view of another illustrative embodiment of alower tip section 22. In this particular view, the solid tip sectioncontains a joint end 18 with four convex semicircles that slide into thecoupler insert 8 which then is bonded into the upper shaft section 7.The head bond end 18 also is configured with four convex semicirclesthat will slide into a coupler insert 8 which is then bonded into thehead 5. This is an example of a bond end designed for a “Plumbers Neck”5 or female bore into the head itself If a second coupler insert is notutilized, a head bond end 16 may be provided (e.g., as in FIG. 8A), andeither 16 or 18 may be optionally provided with a feature that mayfunction as a means for glue relief (e.g., as described above inconnection with FIG. 4A). As shown by the contrast between the darkerand lighter areas of this view, the flutes contained within this designare recessed from the outer surface of the lower tip section. Theseflutes or troughs extend only in the non-bond area and extend from thetip of the lower tip section up to the bond joint region where the twoshafts are bonded together.

As described above, lower tip sections according to embodiments of theinvention can have various combinations of cross-sectional geometry,joint end and head bond end. For example, FIG. 14B shows a fluted lowertip section 22 with head bond end 19 analogous to FIG. 14A, but with asmooth joint end 15 that is configured to slide into a coupler insert24.

FIG. 16A is a cross-sectional view of the radial geometry of the lowertip section 22 examples according to some embodiments. In thisconfiguration, the radial cross section is fluted which consists of sixchannels (flutes) that are equal distance apart and also taper from thehead bond end increasing in depth and width up to the termination of thebond joint end where the upper and lower shaft sections are bonded. Itis conceived that there are multiple variants possible of the radialcross-section covered for this invention. It is also expected that mostif not all of the lower tip sections are tapering from the head bond endand increasing in diameter to the bond joint end where the upper andlower shaft sections are bonded together.

In other illustrative embodiments, as shown for example in FIG. 16B, thelower tip section 22 may be hollow (e.g., analogous to the hollowcircular cross section shown in FIG. 10B and the hollow hexagonal crosssection shown in FIG. 13B). FIGS. 14C, 14D, and 15B show embodimentsanalogous to those depicted in FIGS. 14A, 14B, and 15A, respectively,but wherein the lower tip section 22 has a hollow cross section in theradial direction (as indicated by the dotted lines).

FIG. 17 is an isometric view of an illustrative embodiment of a lowertip section 23. In this particular view, the solid tip section containsa joint end 18 with four convex semicircles that slide into the couplerinsert 8 which then is bonded into the upper shaft section 7. The headbond end 18 also is configured with four convex semicircles that willslide into a coupler insert 8 which is then bonded into the head 5. Thisis an example of a bond end designed for a “Plumbers Neck” 5 or femalebore into the head itself. If a second coupler insert is not utilized, ahead bond end 16 may be provided (e.g., as in FIG. 8A), and either 16 or18 may be optionally provided with a feature that may function as ameans for glue relief (e.g., as described above in connection with FIG.4A). This configuration 23 is an example of a longitudinal complexdouble bend geometry that is commonly used for putter shafts by creatingan offset with the head itself.

FIG. 18A is an isometric view of another illustrative embodiment of alower tip section 23. In this particular view, the solid tip sectioncontains a joint end 18 with four convex semicircles that slide into thecoupler insert 8 which then is bonded into the upper shaft section 7.The head bond end 19 is a smooth surface with a hole drilled in thecenter that is bonded over the head post 11. This is an example of abond end designed for “Over Post” 11 head designs. If a second couplerinsert 8 is utilized, a head bond end 17 may be provided (e.g., as inFIG. 9A). This configuration 23 is an example of a longitudinal complexdouble bend geometry that is commonly used for putter shafts by creatingan offset with the head itself.

As described above, lower tip sections according to embodiments of theinvention can have various combinations of cross-sectional geometry,joint end and head bond end. For example, FIG. 18B shows a lower tipsection 23 with head bond end 19 analogous to FIG. 18A, but with asmooth joint end 15 that is configured to slide into a coupler insert24.

FIG. 19 is a cross-sectional view of the radial geometry of the lowertip section 23 examples according to some embodiments. In thisconfiguration, the radial cross section is circular. It is conceivedthat there are multiple variants possible of the radial cross-sectioncovered for this invention. It is also expected that most if not all ofthe lower tip sections are tapering from the head bond end andincreasing in diameter to the bond joint end where the upper and lowershaft sections are bonded together.

In some embodiments, the tip section of the two-piece shaft may bereinforced with a metal or alloy. The metal or alloy may be provided invarious forms including, but not limited to, a mesh (e.g., as describedin U.S. Patent Application No. 17/165,721) or a rod (e.g., a titaniumretaining rod), and may span the entire length of the lower tip section,or may be provided on one or more portions of the lower tip section. Forexample, as shown in FIG. 20A, in some embodiments a layer of stainlesssteel metal mesh 42 may be provided, which spans the circumference andlength of the tip section. As shown in FIG. 20A, the tip section ishollow circular, analogous to the embodiment shown in FIG. 8D (tipsection 14 with joint end 15 and head end 16), but in other embodimentsany of the lower tip sections described and shown herein may besimilarly reinforced with metal. Adding a reinforcement such as a woven,knitted metal mesh alloy like stainless steel, titanium or aluminum tothe inner circumference of the tip section of a two-piece golf shaftaccording to embodiments of the present invention during the moldingprocess can help to further improve durability, stiffness, and theability to alter the weight distribution on the tip section. Embeddingthe mesh material into the chopped carbon fiber/thermoplastic materialof the tip section can dramatically improve the strength, spine, andtorsional deflection of the tip section. Adding the mesh to the choppedcarbon fiber/thermoplastic material during the molding process can alsoallow the tip section to utilize a lower density carbon fiber. Varyingthe number of wraps of the woven alloy mesh as well as the length of themesh can alter the gradient of density throughout the tip section bychanging the volume of metal mesh added to tip section.

In some embodiments, the metal reinforcement may comprise a woven metalmesh as described in U.S. patent application Ser. No. 17/165,721, whichcomprises stainless steel, nickel, titanium, copper, aluminum,magnesium, or an alloy thereof, and has at least 150×150 wires persquare inch. In some embodiments, the woven metal mesh comprises wirehaving a diameter of about 0.001 inches to about 0.008 inches. In someembodiments, the woven metal mesh comprises wire having a diameter lessthan or equal to 0.001 inches. In various embodiments, the woven metalmesh may have, for example, a plain weave, Dutch weave, twilled weave,twilled Dutch weave, reverse Dutch weave, or five heddle weave. In someembodiments, the woven metal mesh may be annealed.

FIG. 20B is an isometric view of another illustrative embodiment of alower tip section 14. In this particular view (analogous to FIG. 8A),the solid tip section contains a joint end 18 with four convexsemicircles that slide into the coupler insert 8 which then is bondedinto the upper shaft section 7. The head bond end 16 is a smooth surfacewith the absence of a hole drilled into the tip. This is an example of abond end designed for a “Plumbers Neck” 5 or female bore into the headitself. The contrast between the darker area located at the head bondend 16 of the lower tip section 14 and the lighter shading at the bondjoint end 18 represents a gradient in material density along the length28. This demonstrates the ability to not only have a range of densitieswithin a given lower tip section design, but the ability to change thelongitudinal density from one end to the other end of the lower tipsection.

As will be understood by one of ordinary skill in the art, the materialdensity may be varied for any of the lower tip sections described andshown herein. For example, FIG. 20C shows a lower tip section 14 withjoint end 15 and head bond end 16 (analogous to FIG. 8B), which has agradient in material density along the length 28.

FIG. 21 shows a side view and two isometric views of the coupling insert8, according to various embodiments of the invention. The side view ofthe coupling insert 8 shows that the length 30 (dl) of the insert canvary between one-half inch in length up to three inches in length with apreferred embodiment being approximately two inches in length. At theone end exists a flange 29 that flushes up with both the correspondingouter diameters of both the upper shaft section 7 and the respectivelower tip section. Details 33 and 34 are shoulders that are preferablywithin 0.0005 inches under the inner diameter of both the bore hole inthe head itself and the upper shaft section 7. This creates a virtualinterference fit between the coupling insert and the upper shaft and isthe primary method of centering the coupling insert into the shaft orhead so that the axial straightness is maintained. These sections extendfor approximately 0.010 inches in length, but can be longer depending onthe overall length of the coupling insert 8. The center section 32 is anarea of the coupling insert where the adhesive glue is applied for thebond joint. The graphical views of FIG. 21 show a knurled surface alongthe length (d3) whereby the peak of the knurl is at the same outerdiameter as the two shoulders 33, 34. The valley of the knurled surfaceextends to minimum of 0.010 inches in depth compared to the maximumdiameters of 32, 33, 34. Feature 31 represents the outer diameter (d2)of the shoulders 33, 34 and the knurled surface 32. The two isometricviews of coupling insert 8 show both ends of the coupling insert and howthe convex semicircular four-hole design extends from both ends of theinsert 8. These concave semicircles are configured to accept the lowertip section bond joint end containing the four semicircular convexridges to create a mechanical interlock between the upper shaft sectionand the lower tip section. In certain preferred embodiments, thecoupling insert 8 is made out of aluminum or other metallic alloys, butis not limited to those materials, and in other embodiments may beformed from an injection moldable carbon fiber reinforced thermoplasticresin (e.g., KyronMAX) or other reinforced thermoplastic materials.

FIG. 22 is an end view 35 of the flange end of the coupling insert 8.This view shows the location and equal distance spacing of the foursemicircular concave grooves 36 that are configured to accept the foursemicircular convex ridges contained, for example, on the joint end 18of the lower tip section. It is conceived that there are other alternategeometries that may be used to create an interlocking design, howeverthis design is an example of a preferred embodiment.

FIG. 23 is an end view 37 of the insertion end of the coupling insert 8.This view shows the location and equal distance spacing of the foursemicircular concave grooves 36 that are configured to accept the foursemicircular convex ridges contained, for example, on the joint end 18of the lower tip section. It is conceived that there are other alternategeometries that may be used to create an interlocking design, howeverthis design is an example of a preferred embodiment.

FIG. 24 is an end view 38 of the geometry of the bond joint end 18 ofthe lower tip section containing four semicircular convex ridges 39 thatare contained at the bond joint end of the tip section and in someconfigurations also located at the head bond end of the lower tipsection. The four semicircles depicted are designed to act as acentering mechanism between the lower tip section, the coupling insert8, and the upper shaft section 7. These ridges 39 also create amechanical locking bond joint for added joint strength.

FIG. 25 shows a side view, cross-sectional view, end view, and twoisometric views of the coupling insert 24, according to variousembodiments of the invention. Illustrative dimensions of this embodimentare marked in mm. As shown, the length of the coupling insert 24 isapproximately 69.77 mm (2.75 in). At the one end exists a head portion25 (20.27 mm; 0.798 in) that flushes up with the corresponding outerdiameters of both the upper shaft section 7 and the respective lower tipsection. As shown the inner diameter of head portion 25 is 11.93 mm(0.470 in) and the outer diameter is 14.224 mm (0.56 in). Stem portion26 (49.50 mm; 1.95 in) is configured for insertion into the uppersection 7 essentially as described above for coupling insert 8. The twoisometric views of coupling insert 24 show both ends of the couplinginsert. As shown, for example, in the cross-sectional view taken alongA-A and the end view 27 of the insertion end of the coupling insert 24,both the head portion 25 and the stem portion 26 have a smooth interiorsurface configured to accept a smooth joint end 15 on the lower tipsection of the shaft. In certain preferred embodiments, the couplinginsert 24 is made out of aluminum or other metallic alloys, but is notlimited to those materials, and in other embodiments may be formed froman injection moldable carbon fiber reinforced thermoplastic resin (e.g.,KyronMAX) or other reinforced thermoplastic materials.

FIG. 26A illustrates a golf club set of irons 40 comprising hybridshafts according to embodiments of the present invention 3 assembledinto a set of iron heads 6. Shafts according to embodiments of thepresent invention 3 can be constructed based upon many variantsdescribed herein (see, e.g., FIG. 26B which shows an iron shaftanalogous to the putter shaft of FIG. 4B). This illustration depicts apossible scenario whereby the length of the lower tip section and thelength of the upper shaft section can be oriented to be in a descending,ascending, or constant location throughout a set of irons. What isuniform is that the hybrid shaft would still be bonded in the samefashion with the same coupling insert. The length and location of thelower tip section relative to the upper shaft section is determined bythe desired performance of the club itself and the type of player thatthe club is designed for.

FIG. 27A illustrates a golf club set of drivers and fairway woods 41comprising hybrid shafts according to embodiments of the presentinvention 4 assembled into a set of driver heads 44. Shafts according toembodiments of the present invention 4 can be constructed based uponmany variants described herein (see, e.g., FIG. 27B which shows a drivershaft analogous to the putter shaft of FIG. 4B). This illustrationdepicts a possible scenario whereby the length of the lower tip sectionand the length of the upper shaft section can be oriented to be in adescending, ascending, or constant location throughout a set of driversand fairway woods. What is uniform is that the hybrid shaft would stillbe bonded in the same fashion with the same coupling insert. The lengthand location of the lower tip section relative to the upper shaftsection is determined by the desired performance of the club itself andthe type of player that the club is designed for.

While there have been shown and described fundamental novel features ofthe invention as applied to the preferred and illustrative embodimentsthereof, it will be understood that omissions and substitutions andchanges in the form and details of the disclosed invention may be madeby those skilled in the art without departing from the spirit of theinvention. Moreover, as is readily apparent, numerous modifications andchanges may readily occur to those skilled in the art. For example,various features and structures of the different embodiments discussedherein may be combined and interchanged. Hence, it is not desired tolimit the invention to the exact construction and operation shown anddescribed and, accordingly, all suitable modification equivalents may beresorted to falling within the scope of the invention as claimed. It isthe intention, therefore, to be limited only as indicated by the scopeof the claims appended hereto.

What is claimed is:
 1. A two-piece golf shaft, comprising: a hollowupper section; a hollow or solid lower section; and a coupling insertconfigured to join the upper section and the lower section together,wherein the lower section is formed from an injection-molded carbonfiber-reinforced thermoplastic material, and wherein the coupling insertcomprises a hollow structure configured to fit into an inner diameter ofthe upper section and configured to receive an end of the lower sectioninserted therein.
 2. The two-piece golf shaft of claim 1, wherein thecarbon-reinforced thermoplastic material comprises short length choppedcarbon fiber and thermoplastic resin.
 3. The two-piece golf shaft ofclaim 2, wherein the carbon-reinforced thermoplastic material comprisesabout 30% to about 50% chopped carbon fiber.
 4. The two-piece golf shaftof claim 2, wherein the carbon-reinforced thermoplastic materialcomprises a polyamide thermoplastic resin or derivative thereof
 5. Thetwo-piece golf shaft of claim 1, wherein at least one end of the lowersection has an exterior surface configured to mate with an interiorsurface of the coupling insert.
 6. The two-piece golf shaft of claim 5,wherein the exterior surface of at least one end of the lower sectionand at least a portion of the interior surface of the coupling insertare smooth.
 7. The two-piece golf shaft of claim 5, wherein the exteriorsurface of at least one end of the lower section comprises a pluralityof convex ridges configured to mate with a plurality of concave grooveson the interior surface of the coupling insert.
 8. The two-piece golfshaft of claim 1, wherein the coupling insert is formed from a machinedmetal or alloy.
 9. The two-piece golf shaft of claim 8, wherein thecoupling insert comprises aluminum, titanium, or stainless steel. 10.The two-piece golf shaft of claim 1, wherein the coupling insert isformed from an injection-molded carbon fiber-reinforced thermoplasticmaterial or metal mesh composite material.
 11. The two-piece golf shaftof claim 1, wherein the coupling insert includes a flange or headportion on one end, the flange or head portion configured to form abridge that is visible between the upper section and the lower sectionafter they are joined together.
 12. The two-piece golf shaft of claim 1,wherein the coupling insert has an exterior surface comprising at leastone shoulder configured to provide an interference fit with the innerdiameter of the upper section.
 13. The two-piece golf shaft of claim 1,wherein the coupling insert has an exterior surface comprising a knurledsurface on at least a portion thereof.
 14. The two-piece golf shaft ofclaim 1, wherein the lower section has a cross-sectional shape that iscircular, hexagonal, octagonal, or fluted.
 15. The two-piece golf shaftof claim 1, wherein the lower section is hollow.
 16. The two-piece golfshaft of claim 1, wherein the lower section is tapered, decreasing indiameter from a proximal end toward a distal end thereof.
 17. Thetwo-piece golf shaft of claim 1, wherein the lower section is moldedinto a non-linear shape with a variety of longitudinal axes.
 18. Thetwo-piece golf shaft of claim 1, wherein the lower section has a densityranging from about 1.2 grams/cubic centimeter to about 10 grams/cubiccentimeter.
 19. The two-piece golf shaft of claim 1, wherein the lowersection has a density gradient, whereby the density increases from aproximal end toward a distal end thereof
 20. The two-piece golf shaft ofclaim 1, wherein the lower section includes a metal mesh or rod.